1. Field of the Invention
This invention is directed to the field of rotary fluid pumps.
2. Description of the Prior Art
Prior art rotary fluid pumps such as vacuum pumps and hydraulic pumps widely used generally comprise a cylindrical center housing 2 within which an eccentrically rotating rotor 4 provided with a plurality of vanes 3 movable up and down is encased, as shown in FIG. 1.
In these fluid pumps of this type, however, the rotor 4 is placed in a state of suction, at the time of pump suction of fluids, by the presence of negative pressure in an inlet chamber in cooperation with pressure on exhaust side.
Accordingly, the rotor 4 is one-sided and as a result, the shaft and bearing tend to receive an eccentric load.
For this reason, the shaft and bearing have their service life greatly shortened and many attempts have been made to improve the rotary fluid pump of this type.